This invention concerns a process and circuitry for controlling and regulating a motor with a permanent magnetic rotor.
Low-frequency, electromagnetically excited step-by-step switching mechanisms, excited or synchronized oscillator systems, step-switch motors, and synchronous motors are used as electromechanical transducers for time-keeping devices such as quartz clocks, which transmit a stepped-down quartz frequency to a display device. The synchronous motors are driven with an exciter frequency in a self-starting or non-self-starting mode. Such reactive synchronous motors have at least one field coil, to which is applied a synchronous a.c. voltage for the rotary motion of the magnetic field that is generated by the rotor.
Self-starting synchronous motors have a disadvantage of high power consumption. If they are driven by a battery, this involves either a frequent change of battery or batteries of too large a size. Both features are especially undesirable for watches or clocks. Besides the disadvantage of high power consumption, self-starting synchronous motors have the further disadvantage that a pulse that is lost by a pole-jump can no longer be recovered. Such a system cannot keep constant the number of revolutions in a prescribed time interval. Non-self-starting motors can no longer start by themselves if they come to rest during operation, but rather must be restarted by means of a mechanical cranking of the rotor. In addition, with synchronous motors which are cranked, care must be taken that the pointer is precisely adjustable.
With rotating step-by-step switching mechanisms (stepping motors), the motion of a permanent magnetic rotor with n pole pairs, in a stator field that is excited by a.c. or d.c. current pulses, is always used a half or a whole pole-pair step at a time. Step-by-step switching motors with permanent magnetic rotors have a relatively high torque, because of the high magnetic field. They also have high efficiency, and they allow a large step angle when the step motion is suitably damped.
From the literature reference, G. Glaser: "The Technology of Quartz Watches" (Wilhelm Kempter KG, Publishers, 1979, pages 142-161, especially page 153), an arrangement is known which regulates the phase between a quartz oscillator and an electromechanical transducer (motor). With this known arrangement, a phase comparison is performed between the phase of an appropriately stepped-down signal of a nominal frequency delivered by the quartz oscillator and the phase of a signal of an actual frequency that is tapped from the electromagnetic transducer. A particular energy intake per motor period corresponds to every value of the measured phase difference. In this way, a stable phase position of the motor signals establishes itself with reference to the signals from the nominal frequency, depending on the load of the motor. The synchronization signal, that is the nominal frequency signals, can be conducted through an additional synchronization coil, or they can be applied directly additionally to the driving coil, or they can be added to the driving pulses through a circuit. Another, technically more favorable solution is to measure the phase position between the transducer and synchronization signals through a monostable or bistable multivibrator stage, and to control the pulse width of the driving pulses (pulse width control).